Field of the Invention
The present invention relates to a flow control valve including a resin housing.
Background Art
A flow control valve known in the art switches its passageways or regulates the flow rate by moving a valve member arranged inside a housing. The valve member is connected to one end of a valve stem. To move the valve member, the other end of the valve stem is driven by, for example, an electric motor installed outside the housing.
When the flow control valve is left with water remaining inside, the water can freeze and increase its volume, generating an excessively large pressure applied to the housing. Conventional flow control valves include metal housings to withstand such excessive pressure applied during freezing. To achieve lighter weight and other performance, recent flow control valves may include resin housings, which are less strong than metal housings and thus can break under high pressure applied during freezing.
A technique has been developed to avoid breakage of a resin housing by allowing a mounting plate for an electric motor or the like to deform plastically to release pressure applied during freezing before the housing breaks (Japanese Unexamined Patent Application Publication No. 2006-292131). However, if water remaining in the housing freezes quicker in areas near the mounting plate than in other areas, the mounting plate cannot deform plastically and cannot release excessive pressure generated in the housing as the freezing proceeds. In this case, the housing can break. Another technique has been developed to allow water to freeze slower in areas near the mounting plate than in other areas by providing a heat insulating layer of air around water near the mounting plate in the housing (Japanese Unexamined Patent Application Publication No. 2012-219877).
Although these techniques can be used to avoid breakage of housings caused by freezing, resin housings are less strong and can break under large external impacts.